a brief history of fiber lasers - creol.ucf.edu · a brief history of fiber lasers bryce samson 1....

CREOL Affiliates Day Presentation: 7th March 2014

A brief history of fiber lasers

Bryce Samson

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Outline

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• About Nufern• Growth Areas for Specialty Optical Fibers• Trends in high power fiber lasers• Double‐clad fibers for fiber lasers• Recent developments in fibers for fiber lasers• Some example programs between universities and Nufern• Conclusions

About Nufern

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• Venture Capital funded: April 2000– As a telecom fiber company (as are many fiber laser companies!!)

• Purchased Redfern Fibers (Sydney Australia)• Connecticut USA plant on line June 2001• First LMA (laser fiber) developed 1999• Sold to Rofin (A US company, NASDAQ: RSTI) in 2008

– A Fiber laser & amplifier company

• Purchased Optelecom (gyro coil winding) 2010• Plant expansion 2012, now 100,000 ft2

• 150 employees & growing

Nufern Business Components Today

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Raw OpticalFiber

IndustrialLasers

Defense &Aerospace

Sensor

Fiber Business

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5 Families:• DC Fibers• PM Fibers• SM Fibers• MM Fibers• Assembled

Fibers

Double‐clad fibers

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• The growth in double‐clad fiber sales is directly tied to growing sales in the fiber laser & amplifier market

• Since 2001 when Nufern introduced the first set of fibers targeting researchers in the fiber laser community, we have introduced more than 100 different DC fibers (some were successful, some were not!)

• These include Yb, Er, Tm, Ho and Nd‐doped fibers with different core and clad diameters as well as polarization maintaining (PM) fibers

Double‐clad fibers

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• Standardization of DC fibers has been critical to help grow fiber laser market• Multiple suppliers of the same standard DC fibers has helped with component

availability & standardization which has driven down the cost of making a fiber laser

• Output power from a near single mode Yb‐doped fiber “laser” increased from ~100W to >10kW in ~10 years (2000‐2010)

• Output power at “eye‐safer” wavelengths started to catch up….now stands at 1kW at 2m

High Power Fiber Laser Progress 2000‐2010

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So what happened before year 2000?

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• First Nd‐doped glass fiber laser demonstrated early 1960’s, – Elias Snitzer et al., (1961 theory, 1964 Koester and Snitzer)

• First end pumped fiber laser using a laser diode (Stone and Burrus), 1974• First Single‐mode Nd‐doped fiber laser, (Mears et al. Southampton) 1985• Invention of cladding pumped fiber design (Snitzer et al.) 1988.

• Yb‐doped fiber lasers proposed as a viable alternative to Nd‐doped fiber lasers at 1m (D. Hanna et al., Southampton Uni.) 1995‐97

• At a time when everyone was studying Er‐doped fibers for telecom EDFA’s

• The major innovation in this period was the concept of cladding pumping, not to be fully appreciated by the laser community until ~15 years after its invention

The early days of Yb‐doped fibers

• Yb‐doped fiber lasers highlighted in a key paper (H. Pask et al, IEEE J. Selected Topics in QE, 1995)

• This paper contains the first cladding (diode) pumped Yb‐fiber laser, operation from 980nm to 1100nm & single frequency laser performance using an FBG laser cavity

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• SDL (now JDSU) demonstrate a 110W Yb‐doped DC fiber laser, (1999)• Their technology lead was based on the high power & brightness diodes

operating at 9xx ideal for pumping Yb fibers • Arguably this is still true 15 years later!

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For an excellent review of the state of the art diodes in 2000, see IEEE Journal J. Selected Topics in QE, 1995 :


• Even IPG used SDL diodes in those days:

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SDL to Supply Multimode Pump Lasers to IPG PhotonicsDec 04, 2000 Source: SDL, Inc. Two-Year Supply Agreement Totals $66.7 Million

San Jose, CA. SDL, Inc. (Nasdaq: SDLI - news) has entered into an agreement with IPG Photonics Corporation of Sturbridge, Massachusetts to provide high volumes of multimode pump lasers for an array of cladding-pumped fiber product offerings by IPG. Under the terms of the agreement, SDL will supply IPG Photonics with substantial quantities of multimode pump lasers through December 31, 2002. Revenues from this agreement are expected to total $66.7 million over the period.

SDL's multimode pump lasers borrow from the technology used in the company's leading 980 nm singlemode laser diodes designed for terrestrial and undersea telecommunications systems. Multimode pump lasers utilize a broad emitting aperture to allow operation at power levels as high as several watts, and are used as cooled or uncooled optical pump sources for active, cladding-pumped fibers. SDL's new 6380 multimode pump laser represents state-of-the-art technology, offering twice the power from the same aperture size as previous product designs, without sacrificing reliability. Extensive life testing of this device validates this claim. These and other SDL multimode pump lasers will be employed in IPG Photonics' industrial fiber lasers, Raman fiber lasers, and various optical amplifier products used in fiber optic communication systems, terrestrial wireless optical networks and free space communications. These will also be used in IPG Photonics' new generation of low-cost metro amplifiers for use in the emerging metro access networks.

``We chose SDL pump lasers due to their superior performance and reliability, and the company's engineering support and ability to deliver our requirements in time,'' commented Dr. Valentin Gapontsev, Chairman and CEO of IPG Photonics. ``We look forward to our association with SDL over the coming years.''

Silica Optical fibers: The heart of high power fiber lasers

• Core = doped silica glass, carries the single mode signal light, typical size: 10‐30m

• Cladding = Undoped silica glass, helps confine the signal to the core by providing the optical waveguide (lower refractive index) and makes fiber bigger & stronger for handling, typical size: 125‐400 m (~diameter of human hair)

• Coating = Acrylate, for protection & handling, typical size: 140‐550m (typically 2 different layers)

CoreCladding

Coating

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Double‐clad fibers: The heart of high power fiber lasers

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• Rare earth is doped into the core of the optical fiber along with the modifier element (Al, Ge, P, etc)

• Create two waveguide regions: the core and the inner cladding – both guide light.

• Inner cladding waveguide created by making lower index region outside of inner cladding (double‐clad) by replacing the coating with a fluoropolymer low‐index coating.

Double‐clad fibers: The heart of high power fiber lasers

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• Double‐clad fibers increase the ability of the core to absorb light by allowing higher input pump powers enhancing interaction between active ions in the core and the pump light. Shaped cladding used to increase light‐ion interaction.

Standard Fiber

Active core absorbs pump light energy!

Double-Clad FiberInner cladding

Outer cladding

PLMA =LMA =

The first 1kW near single mode fiber laser (2004)

• The first 1kW near single mode (M2 ~3.4) fiber laser was demonstrated in 2004 (ORC, University of Southampton) using free space laser cavity

• HR mirror and 4% Fresnel reflection from the fiber endface formed the cavity

Y. Jeong et al, Electron. Lett, 2004

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Part III: Example fiber laser and amplifier platformsProgress on all‐fiber monolithic kW fiber lasers

Y. Xiao et al, Optics Express, Jan 2012

• Complete monolithic fiber lasers now routinely operate at >1kW output power based on Large mode area (LMA) Yb‐doped fiber & LMA FBGs spliced together

• High slope efficiency and good beam quality at high power level

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Fiber Lasers have overtaken DPSSL in sales and are approaching CO2 annual sales

• Overall the laser market was worth >$2B/year in 2012• Fiber lasers have ~25% of the market• In 2012 fiber lasers had the highest growth (16%) of all categories• Fiber lasers continue to grow in 2013/4 with expectation of 7% growth

Source: David Belforte, ILS, PW Marketplace Seminar

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Examples of Applications: Cutting & Welding using Fiber Lasers

rofin video.mpeg

2 m

…

IPG connector

270 W, 1018 nm SM Fiber Lasers

FBG HR FBG OC

Pump LDs

1 kW

Delivery FiberCore diameter 40 µm

…

57/1 Pump CombinerPump LDs

Master Oscillator

High Power AmplifierLength 15 mCore diameter 30 µmEff. mode area 700 µm2

10 kW

YLS-5000-SM

YLS-10000-SM

Pump lasers quantity

24 47Effective mode area

500 µm2 700 µm2

Delivery fiber length

5 m 2.5 m

YLS-10000-SM Optical SchematicYLS-10000-SM Optical Schematic

Early days of pulsed fiber lasers (1993)

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• Multistage fiber amplifier (3 stages) including large core fiber in the final stage EDFA

• Seeded MOPA using early telecom components

• 110kW peak power generated

Pulsed Fiber laser market now worth >$300M/year

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• In some markets fiber lasers are the dominant laser technology, one example is the marking and engraving segment (~$360M in 2012)

• Overall market share for fiber lasers was ~75%• This is primarily pulsed fiber lasers competing

against DPSSL and CO2 lasersTotal: $359 million

Source: David Belforte, ILS, PW Marketplace Seminar

DC Fiber evolution from 2000‐2010: LMA fibers

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• Most high power fiber lasers are using 250 or 400m cladding• Allows for enough pump power to be coupled into the cladding• In order to keep fiber length short, core diameter is also large

Core/Clad diameter

5m 10m 15m 20m 25m 30m

130um 0.55dB/m (23m)

1.3dB/m (10m)

1.8dB/m (7m)

2.8 dB/m (4.5m)

N/A N/A

250um N/A N/A N/A N/A 1.6 dB/m (8m)

1.7 dB/m (7m)

400um N/A 0.2dB/m(65m)

N/A 0.4 dB/m (12m)

0.6dB/m (21m)

915nm absorption of standard Yb-doped fibers

DC Fiber evolution from 2000‐2010: LMA fibers

• In many pulsed applications it is desirable to use a larger core diameter• This allows for an increased mode field for LP01 mode• Which reduces the effects of non‐linearities in the fiber • Also increases energy storage in the fiber• However the beam quality can deteriorate as higher order modes propagate in

the fiber

Assuming 0.06 NA

CoreØ [µm] 12 15 20 25 30 35

MFD@1080nm [µm] 13 15 18 21 25 28

# of modes 1 2 2 4 6 7

MF-area [µm2] 142 176 255 356 476 616

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Tm‐doped fibers for 2m operation

• 1.5µm and 2µm have become important wavelengths of operation because of the need for eye‐safer operating wavelengths in some cases (>1400nm)

• 2µm fiber lasers based on Tm‐doped fibers are seeing significant growth

• Applications include medical, sensing and materials processing as well as military and defense

0

5

10

15

20

25

1800 1850 1900 1950 2000 2050 210

p(

)

Tm-fiber laser tuning curve (Soton Uni)

wavelength

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• By optimizing the fiber composition, efficiencies of 790nm pumped Tm‐fibers have steadily improved over the last 10 years

• Efficiency for 790nm pumping of Tm‐doped silica is now typically around 60%

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• Tm‐doped fibers have operated at 1kW output power, pumped at 790nm• Delivering good beam quality from standard LMA Tm‐ doped fiber in 2‐stage

MOPA system6-Pumps 790nm6- Pumps 790nm

Active Fiber-Tm doped

Active Fiber-Tm doped

0

200

400

600

800

1000

1200

0 500 1000 1500 2000

Pump Power (W)

Sign

al P

ower

(W)

53.2% slope

T. Ehrenreich et al, Photonics West 2012

Yb‐doped Fiber Developments 2010‐to date

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• Despite the lack of hero high power laser results since 2010, plenty of research has been continuing

• For Nufern investment in Yb‐doped glass & preform design has enabled a understanding of:

• Photodarkening in high power fiber lasers• Multimode instabilities in LMA fibers at high power• Improved low index polymer coatings for reliable high power lasers• Improved manufacturing tolerances in high volume Yb‐doped products


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• Photodarkening is associated with creation of UV defects (color centers) in the core of the fiber when pumped in the IR (say in a Yb‐doped fiber)

• These defects have a long absorption tail extending into the visible and IR causing an increased loss with time when the fiber is pumped

• The rate of the induced loss is related to inversion of the fiber

Data from Liekki Website


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Optics Express 2008

• UV damage in silica fibers depends on the glass composition, in particular the Al and P co‐doping levels


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• In order to operate these LMA fiber based lasers at >1kW, careful optimization of the different fibers along the amplifier chain is necessary– The splice loss between the active and passive fibers, can lead to failure of splices

at high power and deterioration of beam quality at high power levels– This has led to a “matched” series of LMA fibers for high power operation


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• Improved fiber tolerance lowers intracavity splice losses• Which in turn improves slope efficiency (lowers pump requirements) and hence

cost of making the laser• Can improve reliability (splice less likely to fail at high power)

Fiber Bragg grating output coupler

Doped fiberFiber Bragg grating high reflector

Launch pumppower (multimode)

Extract lasing Power (single mode)

Splices


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• Unlike in telecom fibers, the outer polymer coating is a part of the waveguide design of the fiber and requires to be low loss over the life of the fiber

• Optimization of the fluoro-acrylate low index coating has been on going for many years to improve the performance in humid environments

“eyesafe” Fiber Developments 2010‐to date

• Recently interest has grown in the properties of Holmium doped silica fibers • Tuning results for Holmium doped silica shows better operation at longer

wavelengths >2.1m than Tm‐fibers

(A. Hemming et al, CLEO 2013)

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“eyesafe” Fiber Devevelopments 2010‐to date

• In addition, the resonant pumping of Ho‐doped fibers shows promise for power scaling to very high power levels (A. Hemming et al, CLEO 2013)

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Progress on Multimode instability since 2000

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• There are now multiple reports of mode instability in fibers at high power levels, this threshold like behavior appears in different fiber designs from LMA to PCF fibers

• The phenomenon affects the beam quality at high power and threshold depends on the power level, fiber design, inversion level

Progress on Multimode instability since 2000

• Co‐pumped MOPA operating at ~1.5kW using LMA‐YDF fiber and delivering single mode output with no sign of multimode instability (MMI)

• The state of the art in terms of cladding pumped fiber amplifier performance• Made possible by optimization of the Yb‐doped fiber design

0

5

10

15

20

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

Co-Pumped MOPA

Rel

ativ

e Si

gnal

[a.u

.]

Time [msec]

FUD-9049/Lot#: 10-A1501-10-3B-09-0110m/1st ~4.5m in 100mm CoilAbs Length ~17dBMMC: PC-022

445W

785W

1120W

1415W

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Example of university/Nufern collaborations of fiber lasers

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• One of the first collaborations Nufern had was with CREOL on a JTO MRI program to develop Tm‐doped fiber technology

• This included having a PhD student work at Nufern for a summer (Tim McComb)

• Resulted in several publications including one of the first high power Tm‐fiber MOPAs published at the time

Example of university/Nufern collaborations of fiber lasers

• Over the last 5 years Nufern has worked with Prof. Liang Dong at Clemson University to investigate a new fiber technology based on leakage channel fiber design (LCF)

• Interesting technology for scaling mode field in passive & active fibers for generating high pulse energy (and doesn’t require air holes)

• A trend in scaling mode field is required for ultra‐fast fiber lasers• Many of these fiber samples have been sent to other university collaborators

for evaluation (including CREOL)

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Example of recent Nufern collaborations of fiber lasers

• In 2013 Nufern teamed with the Glebov group (Optigrate) to demonstrate 2kW of spectral beam combined power using air cooled VBG technology

• Combined two 1KW beams using Nufern high power kW fiber lasers• Expect the collaboration to provide greater power in the near future

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Future Trends In Fiber Lasers and Collaborations

• The current trend is towards ultra‐fast fiber lasers, with psec and fsec sources receiving a lot of attention

• These lasers places new demands on silica fibers and requires improvements over the current LMA technology

• Hence the trend towards advanced fiber designs such and a trend should continue for the next 5years

• As Nufern grows and diversifies into new markets we expect more (not less) collaborations with universities

• Cost effective way to carry out long term research

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a brief history of fiber lasers - creol.ucf.edu · a brief history of fiber lasers bryce samson 1....

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